and their breadth one palm. O, four pieces of wood, called beaters, of a triangular shape, fixed vertically into the extremities of, and underneath, the arms of the fore-mentioned cross; they are 1 palm in length, and half a palm in thickness, and beat or knead the dough in the tub at unequal distances from the centre. P is a stout wooden tub, about a quarter of a palm thick, well hooped with iron; its diameter is six palms, its height 14 in the clear. Fig. 165 is a box or trough of wood, four palms long, and three wide, in which the leaven is formed (in about an hour) in a stove, and in which it is afterwards carried to the tub P. Fig. 166 exhibits a view of the trundle, cross, &c. with a section of the tub. Fig. 167 is a bird's-eye view of the cross and tub, with the upper ends of the triangular beaters. This tub P will contain about 18 rubbi (about 19 bushels) of flour, which is carried to it in barrels: the leaven is then carried to it in the box or trough, and when the whole is tempered with a proper quantity of warm water, the men work in the wheel till the dough is properly and completely kneaded. In general a quarter of an hour is sufficient to make very good dough; but an experienced baker, who superintends, determines that the operation shall be continued a few minutes more or less, according to circumstances.

The measures in the preceding description are given in Genoese palms, each of which is very nearly equal to 9.85 of our inches. The machinery may be varied in its construction according to circumstances, and the energy of the first mover much better applied than by men walking in a common wheel.

In November, 1811, a patent was granted to Mr. Joseph Baker, navy contractor, for a method of kneading dough by means of machinery. The invention consists in having an upright shaft, turning on a pivot, fixed in the centre of a circular trough, so that the dough placed in such trough may be kneaded by a stone or iron roller, on its edge, passing over it in a rotatory motion, being fixed at a due distance by an horizontal bar or axle to the shaft, which is to be turned by means of one or more other horizontal bars likewise fixed thereto, and worked like a capstan by a proportionate number of bipeds or quadrupeds, such horizontal bars having small shares fixed to them, so as to run in the trough, and, acting like a plough, cause the dough to present fresh surfaces for each successive revolution.

Independent of the methods above quoted, many others might easily be adapted, to do away with the filthy practice to which we have alluded.

THE STEAM-ENGINE.

THE most prominent feature in modern discovery is the steam-engine, which has, with much propriety, been denominated"the noblest monument of human ingenuity." The Marquis of Worcester, who lived in the reign of Charles II., is entitled to the honour of having first directed the attention of mankind to the expansive force of steam when used in a close vessel: but in the book published by him in 1663, he is not sufficiently explicit or intelligible, for us to determine what kind of apparatus, or combination of machinery, was used by him for the guidance of its powers. It is however but reasonable to suppose, notwithstanding the vagueness of his expressions, that it was principally owing to the direction his observations gave to the minds of others that steam began to be used as a first mover of machinery.

When water is exposed to the action of heat, it expands and assumes the gaseous state called steam. When it is confined in a close vessel, and heat is applied to it, the quality of expansion is exerted to a powerful extent; and as the space between the top of the water and the top of the vessel is filled with atmospheric air, the first portion of the power, exerted by the expansion of the steam, is directed towards the displacing of that atmosphere from the situation which its weight had assigned it, and, consequently, such portion of the direct action of the expansive force of steam is to be deducted from its disposable power. This portion of power is, however, ultimately available. For as by a reduction of temperature steam reassumes the state of water, leaving the space which it had occupied again void, the atmosphere which it had displaced returns to its former situation, exerting a force, so to do, exactly tantamount to that which the steam had exerted to displace it. This force may be termed the consequent power of steam. The directing and controlling of these powers, so that they may be applied to the purpose of creating equable motion, is the object attained almost to perfection in the steam-engine: and it is the more accurate control, the more advantageous application, and the more economic production of these powers, that have been aimed at in its various modifications.

For more perfectly illustrating the mode in which steam operates we will suppose the vessel, represented at fig. 168, to be filled with water up to the line A, and the space E occupied with air, and having a plug or piston fitting it at C, and an aperture at D; now if the aperture D be closed, and

heat applied to the water, as at F, steam will be generated, and by its expansive force will raise the piston C upwards; then if the heat be withdrawn and the vessel suddenly cooled, condensation will take place; the steam, reassuming the form of water, will again occupy the space below the line A, and the piston C will return to its place. In this experiment the expansive force of the steam compressed the air in the space E, and forced the plug C upwards, we will suppose, to H; but C, in travelling to H, displaced so much of the atmosphere as occupied the tube from C to H; consequently, the portion so displaced will seek to resume its natural position, and when the force of the steam is withdrawn by condensation, the weight of that portion of the atmosphere will again return the plug Ć to its place; by which, it is obvious, that the raising of the plug was the direct action of the steam, and the returning its consequent action, or the action of the atmosphere in consequence of its having been displaced by the force of the steam.

Again, if we suppose the plug to be in its first situation, as at C, and we open the aperture at D, and apply heat, the steam will rise into the space E, and expel the air through the aperture D, which being closed, "and condensation caused, the space E will be left a vacuum, and the atmosphere seeking to occupy that space will force the plug C down to the line Á; here the movement of the plug C was solely caused by the atmosphere exerting itself to regain the position whence it had been expelled by the force of the steam through D, and this effect is performed by the consequent power of steam alone.

It has been found by experiments, that the pressure of the atmosphere is equal to about 14 pounds weight upon every square inch, so that sup→ posing the superficies of the aperture of the vessel, fig. 168, to contain one square inch, the power exerted by the steam in raising C to H will be tantamount to raising 14 pounds weight that height, together with the power necessary to overcome the friction and weight of the piston C, in the cylinder; and, that the power exerted by the steam in expelling the atmosphere from the space E, and obtaining its consequent pressure to the raising of 14 pounds from A to C; and that the disposable power, obtained by the return of the piston from H, will, in the first instance, be equal to the raising of 14 pounds weight from C to H, less the amount of the friction of the piston C; and, in the second, will be equal to the raising of 14 pounds weight from C to A, less the amount of the friction as before. In both these instances the expansive or direct force of the steam has only been considered as equal to the displacing of the atmosphere, or what will be equal to 14 pounds pressure on each superficial inch; but if the piston C be loaded with any weight, the steam will, if urged with sufficient heat, raise it, always premising that the vessel is strong enough to resist the increased pressure. Suppose C to be loaded with 10 pounds of weight, the steam must be urged until its pressure is equal to 24 pounds, 10 pounds more, 14 pounds the pressure of the atmosphere on each square inch, and the resulting disposable force will be equal to 24 pounds more, the weight of C, less its friction returning to the place from where C was raised; so that, in this case, the pressure on the internal sides of the vessel, tending to burst it, will be equal to 10 pounds per square inch of the internal superficies, the remaining 14 pounds being counteracted by the pressure of the atmosphere on the external surface, which is equal to 14 pounds of the internal pressure. By this, it is evident, that the direct force of steam may be increased without limits, whereas the resulting force or pressure of the atmosphere is manifestly bounded to 14 or 15 pounds on the square inch according as its density varies.

Trusting from this explanation that even those who are unacquainted with matters of this nature will clearly comprehend the manner in which the expansive force of steam operates, we shall proceed to explain the different mechanical combinations which have been formed to render this power subservient to our will: premising that what we have heretofore called the consequent power of steam will, in future, be considered the pressure of the atmosphere, which in fact it is, having adopted the other term in the introductory explanation, in order more clearly to impress on the mind, that the expansive force of steam is actually the only originator of power in this machine.

The first apparatus with which we are acquainted, constructed for the purpose of employing steam as power to act in a close vessel, was invented by a Captain Savary, for which, in the year 1698, he obtained a patent. The form of it, as invented by him, is represented in fig. 169.

u, a close boiler, placed on a furnace, and of sufficient strength to resist considerable pressure; B another vessel strongly constructed; ce a pipe with a cock in it at i, by means of which a communication can be made from a to B at pleasure; e a pipe proceeding downwards into a well or other reservoir of water; ff another pipe proceeding from B to a reservoir placed above; hh is a pipe communicating from В to the pipe ff, and having a cock in it at k to allow of, or cut off, such communication; m is a valve capable of closing the pipe e by pressure from above, and of opening it by pressure from below; 7 a similar valve fitted to the pipe ff, and capable of being acted upon in a similar manner. If the boiler a be filled with water to the dotted line, and heat applied by means of the furnace, the steam will rise in the boiler, and, passing through the pipe e c, fill the vessel B, and pass up the pipe ff; the valve m being shut by the expansive force of the steam pressing upon it: if the cock i be now shut and the steam in the vessel B condensed, by throwing cold water upon its outer surface, the atmosphere pressing on the valve m will close it, and the interior of the vessel B remain a vacuum, and the water in the reservoir to which the pipe e passes will be forced by the external pressure of the atmosphere into the vessel B up to the dotted line, which is supposed to be about 26 feet from the surface of the water in the reservoir, being the length of a column of water, which, taking into account that the vacuum thus formed is not quite perfect, is equal to the pressure that will be exerted by the atmosphere. If the cock ibe opened again, and the steam allowed to press on the surface of the water, in B, it will close the valve m, and cause the water to ascend the pipe ff, through the valve 7, to the upper reservoir; and when the cock i is again shut, and the steam in B again caused to condense, the operation will be repeated, and the weight of the water in the pipe ff will close the valve 1, and cause the vessel B to be filled by e as before.

Such was the construction and mode of operating with the first apparatus made by Captain Savary. But he, finding it inconvenient to cause condensation by means of throwing cold water upon the outer surface, introduced the pipe hh into B, which, by opening the cock k, allowed some portion of the water to pass from the pipe ff, which was always full after the first stroke, and thereby cause condensation more quickly to ensue.

The trial or gauge cocks o, q, were also contrived by Captain Savary, in order to ascertain the height of the water in the boiler. If the surface of the water is above the lower ends of the cocks, and the cocks be opened, water will issue from them; if below, steam. But if the water is at its proper level, that is to say, if the surface of the water be in the intermediate space between the ends of the cocks q and no, water will issue from the former, and steam from the latter. This knowledge was necessary to be obtained; for should the surface of the water exceed the height of the cocks o, there will not be room for a sufficiency of steam to remain in store for continued operation.

The application of this engine was confined to the raising of water to small heights, as it operated only by atmospheric pressure; in deep mines it was found not to be effective. Taking into consideration, however, the then imperfect state of knowledge, so far as regarded steam as a first mover, the inventor is entitled to no inconsiderable degree of praise for this specimen of his ingenuity. The greatest objection to this mode is, the great waste of steam, and consequent unnecessary expenditure of fuel, arising from the condensation being effected by allowing cold water to come into contact with the steam in the vessel B.

At the time when the existence of this engine was first made known to the public, the amazing power of steam, which it so plainly demonstrated, began very deservedly to obtain the attention of ingenious men; and disputes for the honour of the discovery took place, the English ascribing it to the Marquis of Worcester, the French to Papin.

Without entering into the minutiae of this contest, it will be sufficient for us to trace progressively the grand improvements that have taken place in the steam-engine in this country: though not forgetting to mention the accessary improvements derived from foreign aid. Of this latter is the safety valve, an instrument, though in itself simple, of such vast importance, that to it may be attributed the general introduction, and consequent improvement, of the steam-engine to its present existing state of perfection. It was contrived by Dr. Papin, who, at the time of Captain Savary's invention, was making experiments on the power of steam at high temperatures, for the purpose of dissolving bodies. It consists merely of an aperture of a specific dimension, suppose, for instance, one square inch, in or communicating with any close boiler, and a valve properly fitted in that aperture, such valve being on the outside loaded to any extent considered necessary to resist the force of the steam until it has acquired a certain degree of power, computed to be what the boiler is perfectly capable of sustaining without the chance of bursting. Now it is manifest, until the pressure of the steam